Centrifugal calibration device



Feb. 9, 1960 M, E BQURNS rAL 2,924,092

CENTRIFUGAL CALIBRATION DEVICE Filed May 6. 1955 2 Sheets-Sheet 1 Feb. 9, 1960 M E, BOURNS ETAL 2,924,092

CENTRIFUGAL CALIBRATION DEVICE Filed May 6. 1955 2 Sheets-Sheet 2 IN V EN TOR.

United States latent1 CENTRIFUGAL CALIBRTION DEVICE Marlan E. Bourns and Marvin E. Harrison, Riverside, Calif.; said Harrisonassignor vto .Bourns, lInc.

Application May 6,1955, Serial No. 06,622

Claims. (Cl. 731) The present invention relates tofcentrifugal apparatus for testing electrical instruments.

At the present vtime there is considerable .demand for electrical instruments known as accelerometers. These devices are used to measure acceleration, yand usually employ either a potentiometer type Iofelectrical mechanism, a capacitance typefofelectrical mechanism, or what may be termed a slug tuned coil, soas to provide an-e1ectrical output which varies with the rate of acceleration. Itis necessary for .many applications such as for example in guided missile work to calibrate the accelerometers used so as to ascertain the precise -electrical characteristics of these instruments. As `nearly as fis presently known, no completely satisfactory mechanism has been developed for this purpose.

It is an object of this invention 'to provide a centrifugal apparatus for the calibration and testing of accelerometers. A more specific object of the present invention is to provide a .device of the class described which is 'comparatively simple to construct, which is exceedingly effective for .the purpose intended, and which is capable of being used by comparatively inexperienced operators. Further objects of this invention as well as Amany advantagesof it will bemore fully apparent from the remainder :of this specification, the apended claims, and

the accompanying drawings in which:

Fig. 1 is a side elevational view of a centrifugal calibration vdevice of the present invention, a part of this view being Abroken .away so as to reveal certain constructiona'l details;

Fig. 2 is a .cross-sectional -view taken at line 2--2 of Fig. 1 of the drawings;

Fig. 3 is -a partial cross-sectional vView taken at line 3 3 of Fig. 2 of the drawings;

Fig. 4 is a cross-sectional View similar to Fig. 2 showing a modified centrifugal calibrational device of this invention;

Fig. 5 is a side elevational view similar to Fig. l of a second -modied centrifugal calibration device of the invention;

Fig. 6 is a top view of the device shown in Fig. 5: and

Fig. 7 is a detailed view taken on line v7--7 of Fig. 6 of the drawings.

In all figures of the drawings like numerals are used to designate like parts wherever convenient for purposes of illustration and explanation. It is to be understood that the accompanying drawings do not represent the precise proportional `sizes of the various parts employed with the instant invention.l Rather, the sizes of these parts illustrated are chosen so as .to most conveniently Vand lucidly illustrate vthe essential features of the present invention and inventive concept.

The instant invention is considered -to be fully dened or summarized by the appended claims forming a part of `the specification. If desired, however, the present invention may be briey summarized asbeingconcerned with a centrifugal calibration .device Yemploying mounting means; aligned bearing means located upon said 2,924,092 Patented Feb. 9, E960 ice L mounting means; -a shaft positioned betweensaid bearing means; means forturning said shaft; a-test stand .mounted on said shaft so as to project:therefrom;.means Yforfho'ld-l ing an accelerometer mounted .on said .test stand; means forfmoving said means Yfor holding anaccelerometen'said means for moving being mounted ion .said test stand; and means for obtaining f an Aelectrical signal variation from an accelerometer mounted within said :means :for holding said accelerometer.

In Fig. l there is shown -a :complete centrifugal calibration device 10, whichincludes a ,generally grectangular frame 12 designed to be `mounted on `appropriate iegs. Mounted upon-this frame are .two thrust bearings :14 .and 16 having formed therein'alignedfopenings 18 and tapped end openings 20 -and 22. The end opening 20'iszdesignedso as lto receive :and'hold apipe .28 which leads to acontrol box 26 mounted upon the :frame 12. The other rend opening 22 is designed uto-receive a .pipe 24 iwhich l:also leads to the control box 26. Within this .control box there is positioned `an-'appropriate reservoir for hydraulic iluid, a small pump, and a valve manipulated zby ra '.valve handle 32. The purpose of the control lbox is 1oiprovide .means whereby @when the va'lve .handle .32 lprojecting from this box is turned hydraulic uid under pressure may be introduced `into'centeriopenings 34 -and ..36 iformed within a shaft 38. This shaftis, as is bestseen in Fig. r1-

of the drawings, held within the thrust bearings 14 vvand 16 so that the center openings '34 and 36 iare :positionedadjacent to the aligned openings 18.

Mounted upon the shaft 38 immediately adjacentto the thrust bearing 16 is ya stepped pulley Y4x0 of :known type' which is adapted to receive .a V-belt 42 :so that power may lbe transmitted from -a :motor 44 through another stepped pulley 46 attached ,-to -this motor y44 -to the :shaft 38 by the use of this 'V-belt. vPreferably the .motor employed is mounted directly Aupon lthe frame 12 as illus-r trated and is of such a nature ithat the v:speed of this :no1 tor may be very accurately controlled. A suitable motor is a common synchronous A.C. motor. 1

Immediately above the :pulley 40 there is 4secured :to the shaft 38 a test .stand 48. Preferably, this stand iis formed integrally with the shaft 38 by being welded to it. Formed upon the test ystand v48 are housings V50, eachhaving formed therein internal cylinders 52. In )each of theseicylinders -there is located la piston 54 to whichthere is attached a piston rod 56. As is Ibestseen in'Fig. 2 of the drawings, the -piston rods 56 project from `the hous-; ings 50 through openings 58 formed therein. `Inaeach of the housings 50 there are 1ocatedpassages60-and62 connecting the center openings .34 and 36, respectively, with the ends of the cylinders y52 on both sides of the pistons 54. Thus, with this construction as hydraulic uid under pressure `is introduced into the shaft 3.8 :through either the pipe 24 or the pipe 28 by appropriate manipulation of the valve handle 32, the pistons 54 are caused to move within the cylinders 52 `in :synchronism with one another, yso that at all times lthese pistons :are both located an equal distance from the center ofthe shaft 38.

Attached to each of the piston rods 56 are small cans 64 -which are adapted to receive and hold accelerometers being calibrated 'with the centrifugal calibration device 10. Mounted -upon each of the cans 64 are non-conductive brackets `66 formed of appropriate material :such as" for example a filled phenolic resin. Secured to each .of these brackets 66 are live Vseparate resilient electrical contacts 68 of the type commonly employed in poten-l tiometers and like devices. Three of the contacts 'on each bracket are adapted to be connected to appropriate l tacts `on each bracket arevconnecte'd together through the;

use of wire leads 70.

All of the contacts -68 are located upon the brackets 66 in such a manner that they resiliently bear against electrically conductive layers 72 formed upon non-conductive sheets 74 secured within recesses 76 in the test stand 48. Preferably, with the invention, one of the layers 72 on each of the sheets 74 is formed of amaterial having a relatively high resistance. The contacts engaging these high resistance layers are connected to the next adjacent contacts 68 through the use of wire leads 70. All of the conductive layers 72 may be placed upon the sheets 74 through the use of appropriate printed circuit techniques.

It will be further realized by those skilled in the art thatthe layers 72 contacted by the contacts 68 which 1 are connected together through the use of wire leads 70 form what in effect is a complete variable resistor in which an electrical return strip and a resistance layer are placed side by side and in which the conventional slider employed is constituted by the contacts 68 connected together by the wire leads 70. All of the layers 72 are connected by wires (not shown) to slip rings 80 of the same category conventionally employed in alteroating current motors and generators.` The construction of'these slip rings 80 is best shown in Fig. 3 of the drawings where it is seen that each of them comprises a non-conductive ring 82 mounted about the shaft 38 and a conductive ring 84 secured to each non-conductive ring 82.

Electrical take-off from the conductive rings 82 is accomplished through the use of resilient conductive strips 86 mounted upon a non-conductive support bracket 88 secured to the frame 12. These conductive strips 86 resiliently bear against the conductive rings 84. Appropriete wires are used to connect the conductive strips 86 to various instruments of a conventional nature employed with the centrifugal calibration device 10.

' The operation of this centrifugal calibration device is considered to be essentially obvious from the foregoing. In use, accelerometers are -placed within the cans 64 and the terminals of these accelerometers are attached to the adjacent contacts 68. The device is then caused to rotate through operation of the motor 44 and during this rotation the position of the accelerometers with respect to the shaft 38 is adjusted through the manipulation of the valve handle 32, causing the accelerometers to move from immediately adjacent to the shaft 38 to a point at the extreme limit of movement possible with the pistons 54. These accelerometers are then moved back to their starting position through further manipulation of the valve handle 32. As such accelerometers are rotated, the acceleration' to which they are subjected causes them to operate in the intended manner, changing an electrical value from each which is transmitted externally of the device through certain of the layers 72, the wires 78, the slip rings 80, and the conductive strips 86. The position of the 'accelerometers upon the test stand 46 is at all vtimes known through the operation of the variable resistor type of arrangement formed using the contacts 68 connected together by the wire leads 70 and the layers 72 engaged by these contacts.

Another embodiment of the invention is illustrated in Figure 4. Here there is shown a centrifugal calibration device 90 in which an additional piston rod 92 has beenl connected to each of the pistons 54 empioyed, these additional rods passing outwards through openings 58 formed Within the housings 50. These piston rods 92 are preferably manufactured of ferro-electric material. They are designed to move within induction coils 94 mounted upon the test stand 48 immediately adjacent to the housings 50 so as to change the inductance of these coils. These coils are with this modification of the invention connected to slip rings 80 in the'same manner as `the layers 72. l

Those skilled in the art will realize from a consideration of-the'foregoing descriptionr and the accompanying drawings that the test stand 48 and all ofthe means mounted upon this stand are designed in such a manner as to have two separate planes of symmetry, each of these planes being located at right angles to one another and each of these planes passing through the axis of the shaft 38. These planes of symmetry are maintained even during the operation of the centrifugal calibration devices of the invention, this symmetrical arrangement being exceedingly important, for on many occasions it is desired to operate these devices at comparatively high rotational speeds and unless they are symmetrically formed or specially balanced, excessive vibration is apt to occur.

In Figs. 5 and 6 of the drawings a second modified centrifugal calibration device 96 of the invention is shown which has the same symmetrical type of construction described in the foregoing paragraph. This device 96 consists of a base n8 upon which there is mounted a housing 100. Upon the base 98 within this housing properthere is mounted a second bearing 104, which is aligned with the thrust bearing 102 so that these two bearings serve to carry a hollow shaft 106 whichprojects from the housing 100. Positioned around this shaft 106 is a driven gear 108, which is adapted to coact with .a driving gear 110 mounted upon a motor shaft 112. This motor shaft projects from what is preferably a synchronous A.C. motor 114 mounted upon the housing 104.

Thev upper end of the shaft 106 remote from the .housing 100 is attached securely as by welding or the hlfe to a test stand 116 which may be formed out of a single sheet of material. Secured to one end of this test stand 116 is a small electrical motor 118. Secured to th e other end of this test stand is a small helical potentiometer 120. It will be realized from a consideration of Figs. 5 and 6 of the drawings that the motor 118 and the potentiometer 120 are aligned with one another on opposite sides of the shaft 106. Preferably both the motor 108 and the potentiometer 120 are of the same weight so that the test stand 116 is balanced at all times.

Mounted upon bearings 122 secured to the test stand 116 are lead screws 124. These lead screws are thus in this construction mounted parallel to one another and to a line drawn between the motor 118 and the potentiometer 120. The leadA screws are adapted to be driven by meansof a drive gear 126 attached to a shaft 128 projecting from the motor 118; this drive gear 126 coacts with driven gears 130 secured to the lead screws 124. Gears 132 similar to the driven gears 130 are mounted upon the ends of the lead screws 124 adjacent to the potentiometer in such a manner'that as these gears 132 turn they cause another gear 134 attached to a shaft 136 projecting from the potentiometer 120 to turn so as to adjust this potentiometer. It will b e realized from the foregoing that the potentiometer is thus synchronized so as to turn in accordance with the operation of the motor 118.

The lead screws 124 are preferably formed so as to have right and left hand threads, respectively, so that as the motor 118 is operated small carirages 138 mounted upon these lead screws will be driven with respect to the test stand 116 in opposite directions. The carriages 138 are essentially in the shape of boxes having ends provided with threaded apertures 142 adapted to engage the lead screws 124. Small projections are formed on these ends 140 so as to engage guide slots 144 formed within the test stand 116. These giude slots thus serve to p revent rotation of the carriages 138 during the operation of the centrifugal calibration device 96.

The carriages 138 are adapted to contain small accelerometers (not shown), which accelerometers are connected to slip rings 146 located upon a non-conductive sleeve 148 about the shaft 106 within the housing 100 through the use of coiled wires 150, which expand and contract as the carriages 138 are moved upon the test stand ,116: Ctfiall of the slip rings 146 are also connected to other wires 152 leading to the motor 118 and the potentiometer 120. The slip rings are all contacted by means of spring contacts 154 mounted upon a nonconductive block 156. This block is located within the housing 100. Appropriate wires (not shown) are normally employed to connect the spring contacts 154 to various test instruments and controls.

It will be realized from the foregoing description that the centrifugal calibration device 96 presents a very efficient structure for the purpose intended. This device 96 diiers from the embodiments of the invention previously described in that accelerometers located within the carriages 138 may be moved on both sides of the test stand 116 so as to provide for both positive and negative acceleration. The carriages 138 are mounted upon lead screws 124 so that they are at all times symmetrically disposed on opposite sides of the shaft 106.

Obviously a number of modifications may be made in the invention without departing from the essential nature of this invention. As an example of such modifications, various mechanical means can be employed instead of the hydraulic means previously described so as to move accelerometers mounted upon the test stand 48 with respect to the shaft 38. Similarly, it is possible to utilize other electrical means besides the layers 72 for the purpose of taking ot an electrical value from such accelerometers and for the purpose of determining the position of the accelerometers upon the test stand. By special balancing it is possible to form a device capable of Calibrating only one accelerometer at a time. Obviously, a number of separate test stands can be mounted on a single shaft, and more than two accelerometers can `be calibrated on a single test stand.

All of such refinements are considered to be essentially of an engineering nature. The present invention is to be accorded comparatively wide latitude with respect to such engineering renements inasmuch as it is obviously capable of considerable modication. For this reason the invention is to be considered as being limited only by the appended claims forming a part of the disclosure.

We claim:

l. A centrifugal calibration `device for use in calibrating accelerometers which includes: mounting means; aligned bearing means positioned upon said mounting means; a shaft held within said bearing means so as to project therefrom; a test stand mounted upon said shaft; means for holding an accelerometer in position upon said test stand; a lead screw mounted upon said test stand, said lead screw engaging said means for holding accelerometer; means for rotating said lead screw; and means for determining thevposition of said means for holding an accelerometer.

2. A centrifugal calibration device as defined in claim 1 wherein said means for determining the position of said means for holding an accelerometer comprises: a potentiometer operatively connected to said lead screw, said potentiometer being mounted on said test stand.

3. A centrifugal calibration device as defined in claim 2 wherein: said potentiometer is a rotating potentiometer.

4. A centrifugal calibration device as defined in claim 1 wherein said means for rotating said lead screw comprises: a motor, said motor being mounted upon said test stand.

5. A centrifugal calibration device for use in calibrating accelerometers which comprises: mounting means; aligned bearing means mounted upon said mounting means; a shaft held within said bearing means so as to project therefrom; a test stand mounted upon said shaft; a lead screw rotatably mounted upon said test stand; means for rotating said lead screw; means for holding an accelerometer carried by said lead screw; means for determining the position of said means for holding an accelerometer mounted upon said test stand; means for rotating said shaft; slip rings mounted upon said shaft; means for electrically connecting said slip rings with an accelerometer mounted upon said means for holding an accelerometer; and brush means carried by said `mounting means electrically contacting said slip rings.

6. A centrifugal calibration device which comprises: mounting means; aligned bearing means mounted upon said mounting means; a shaft held within said bearing means; a test stand mounted upon said shaft; lead screws rotatably mounted parallel to one another on opposite sides of said shaft on said test stand, said lead screws having adjacent ends; motor means mounted on said test stand adjacent to ends of said lead screws; means connecting said lead screws and said motor means whereby said motor means is operatively` connected to said lead screws; a rotary potentiometer mounted upon said test stand adjacent to the other ends of said lead screws; means operatively connecting said lead screws to said potentiometer whereby said potentiometer is operated by the movement of said lead screws; means for holding an accelerometer carried upon each of said lead screws; and means for preventing rotation of said means for holding accelerometer.

7. A centrifugal calibration device for use in Calibrating accelerometers which comprises: mounting means; aligned bearing means mounted on said mounting means; shaft means held between said bearing means; a test stand mounted on said shaft means; cylinder means 1ocated on said test stand; piston means located on said cylinder means; means for holding an accelerometer located on said test stand; means connecting said means for holding an accelerometer with said piston means whereby said means for holding an accelerometer is moved during motion of said piston means; and means for conveying hydraulic iuid under pressure through said shaft means into said cylinder means so as to move said piston means within said cylinder means.

8. A centrifugal calibration device as defined in claim 7 including means for rotating said shaft.

9. A centrifugal calibration device as defined in claim 7 wherein said means for conveying hydraulic fluid includes: passage means located in said shaft means, said passage means leading from the ends of said shaft means to said cylinder means on different sides of said piston means.

10. A centrifugal calibration device for use in calibrating accelerometers, comprising a support member journaled for rotation in a horizontal plane, means for driving said support member, an accelerometer holder mounted on said support member for movement in a generally radial direction with respect to the axis of rotation, actuating means mounted on said support member and operable to shift said holder to any predetermined position along said support member, and control means separate from said support member and operatively connected with said actuating means to operate the same so as to vary the radial distance of said holder from said axis of rotation and thereby vary the centrifugal force acting upon an accelerometer contained within said holder.

References Cited in the le of this patent UNITED STATES PATENTS 2,052,711 Jennings Sept. l, 1936 2,301,967 Nosker et al. Nov. 17, 1942 2,452,031 Allnutt et al. Oct. 26, 1948 2,503,052 Keinath Apr. 4, 1950 2,655,033 Burrell Oct. 13, 1953 2,737,806 Dart et al. Mar. 13, 1956 2,788,654 Wiancko et al. Apr. 16, 1957 

